Natural Causes of Floods
- Slow rain or snow has the potential to cause flooding if the amount of water being added to a river or stream exceeds the body of water's capacity. This typically occurs in areas that receive prolonged periods of rain or snowfall. Melting snow on warmer days also causes slow floods because it adds to the level of the river or stream slowly, raising the water level over time. Another cause of floods related to melting snow and excessive rain is damming. Mudslides or debris pile up downstream and block the flow of water resulting in a slow flooding effect.
- Some floods caused by heavy rainfall are called flash floods because they happen rapidly. This type of flood occurs when a lot of rain is dumped on an area in a very short amount of time, such as during a bad thunderstorm or hurricane. Mudslides are a common occurrence during flash floods. These flash floods are often devastating because they come on too quickly to take precautions. Most flood-related deaths are caused by flash floods.
- Storm and tidal surges cause coastal tides. Usually the result of hurricanes, cyclones or tsunamis, heavy winds cause ocean swells that are pushed toward land resulting in flooding. While coastal flooding is a particular concern in low-lying areas, it can happen anywhere along a coastline. It is important for residents of coastal regions to keep an eye on the news if a hurricane or tsunami is expected. Those living in low-lying areas may need to evacuate.
- While many dams are man-made structures, there are a variety of dams that are formed by natural causes, including beaver dams, landslide dams and lava dams. These naturally occurring dams are often beneficial to the environment and serve the same purpose of man-made dams --- to block the flow of water. Just like man-made dams, these dams degrade or are damaged over time and usually eventually fail. If the dam was containing an amount of water too great for the downstream body of water, a flood will result.
